This proposal is aimed at understanding the development, rapid function, and localization of CD8+ T cells that respond in the absence of cognate antigen during bacterial infections, with the hypothesis that CD8+ T cells are important contributors to the early, innate production of IFN-gamma. The specific aims are: I: To analyze the survival, localization and protective ability of memory CD8+ T cells vs. NK cells during a Listeria monocytogenes (LM) infection. In this aim we will dissect the differences in protective ability between NK and memory CD8+ T cells responding to LM in a non-antigen specific fashion. We will use immunocytochemistry to analyze the location of the responding populations of transferred cells within the organs targeted by LM infection. In addition, the ability of memory CD8+ T and NK cells to survive after responding to LM will be measured using immunocytochemistry and flow cytometry. II: To determine the role of CD8+ T cells in aiding in the polarization of CD4+ T cells. Our data shows that memory CD8+ T cells rapidly secrete IFN-gamma independent of cognate antigen and thus play an important role in the innate immune response, which is essential in promoting TH1 development through the secretion of cytokines. We will now directly test the ability of CD8+ T cells and NK cells to influence TH1 development by secreting IFN-gamma using co-transfer protocols to analyze the polarization of CD4+ T cells in response to pathogens. III: To analyze the effects of IL-12 and IL-18 on naive and effector/memory CD8+ T cells. In the first part of this aim, we will determine which cytokines, if any, are required in order to establish IL-12/IL-18 responsiveness during the transition of naive CD8+ T cells into primed, effector cells. In the second part of the aim, we will determine the functional outcomes of signaling through the IL-12 and IL-18 receptors and compare that with signaling through the TCR using microarray analysis and real-time RT-PCR. These studies will further our understanding of innate immune responses to pathogens mediated by CD8+ T cells and allow us to better combat infectious diseases.